Oscar-nominated star will appear alongside Shirley MacLaine in season four finale

The Emmy and Golden Globe-winning actor will play Harold Levinson, the "maverick, playboy" brother of Cora Crawley, the Countess of Grantham, according to tvline.com.

It is said that the 46-year-old - currently filming The Amazing Spider-Man 2 - will appear alongside returning guest star and fellow American Shirley MacLaine (who plays Cora's mother Martha Levinson) in the final episode of the fourth series.

Executive producer Gareth Neame is reported to have described Harold as “free-spirited”, promising that the characters played by both Giamatti and MacLaine will “upset the Grantham’s apple cart” in the finale.

The show has recruited several new faces for the fourth series in the wake of several prominent cast departures.